This invention relates to a picture signal reproducing apparatus capable of producing a slow-motion picture signal or slow-motion image signal and, more particularly, to an efficient scheme for interpolating original pictures data such as original frame/field pictures to produce the slow-motion picture signal.
In the art of digital moving picture, digital data representative of a sequence of original moving pictures must be compressed. Generally, large amounts of data art required to define the sequence of original roving pictures. Transmitting/recording of such large amounts of data results in ineffectual use of the resources such as the available radio frequency spectrum. In view of the above, the data must be compressed.
One standard that has been adopted for encoding a sequence of original moving pictures into a compression coded picture data is the Motion Picture Experts Group (MPEC) standard, more particularly, the MPEG-1 (MPEG Phase-1) or the MPEG-2 (MPEG Phase-2) standard. The data coded according to MPEG standard is called "MPEG code" or a "MPEG data". MPEG-1 code is employed in a Video CD and so on while MPEG-2 is employed in digital broadcasting and recording media such as a DVD (digital video disc). Both of MPEG-1 code and MPEG-2 code contain motion vector data. MPEG code is decoded with reference to the motion vector data by a picture signal decompression processor included in a picture reproducing apparatus, to produce the moving picture sequence.
A conventional picture signal reproducing apparatus comprises a picture signal decompression processor, a memory or a display buffer, and a buffer controlling unit. The picture signal decompression processor receives an MPEG code signal having the MPEG code sequence and decodes the MPEG code with reference to the motion vector data to produce a group of decoded pictures corresponding to the sequence of original moving pictures. The display buffer receives the decoded pictures from the picture signal decompression processor and temporarily stores the decoded pictures as reproduced pictures. The buffer controlling unit controls the buffer to read out the reproduced pictures in the order of displaying the reproduced pictures to produce a reproduced picture signal.
The conventional picture signal reproducing apparatus produces a slow-motion picture signal from MPEG code signal, as follows. In case of playing the reproduced pictures in slow motion which has a slow speed corresponding to 1/n of the normal speed, the buffer controlling unit controls the display buffer to repeatedly read out each of the reproduced pictures n times. Namely, in three times slow motion, the picture reproducing apparatus repeatedly produces each of the reproduced pictures three times.
However, the slow notion picture reproduced by the conventional picture signal reproducing apparatus gives a user unnatural impression. A particular one of the reproduced pictures is repeatedly displayed n-times and then in replaced with succeeding one of reproduced pictures. And then the succeeding reproduced picture is also repeatedly displayed n-times. Thus, the user watches, on a display screen, reproduced pictures changing from one to another in a longer period or cycle than a predetermined period at the normal speed. Consequently, the user feels that objects in the pictures on the display screen rapidly move at a time instant when changing from one picture to another picture. As a result, the user has unnatural impression for the moving picture.
Furthermore, a picture signal reproduction apparatus providing smooth slow-motion pictures is disclosed in Japanese Unexamined Patent Publication (JP-A) No. 178270/94. This apparatus is not for decoding compression data such MPEG code, but for processing original pictures themselves. This apparatus analogously processes a plurality of original pictures such as frame pictures to predict motion vectors between the original pictures, thereby producing interpolation pictures by the use of the motion vectors. In order to carry out the above-mentioned processing, this apparatus has a complicated structure and makes no use of digital advantages possessed by MPEG code.